1. Field of the Invention
The present invention relates to a method for producing a molded article of a thermoplastic resin. In particular, the present invention relates to a method for effectively producing a molded article which consists of a thermoplastic resin or comprises a thermoplastic resin core and a skin material layer thereon without the deterioration of appearance.
2. Description of the Related Art
In the production of a molded article of a thermoplastic resin, various improvements have been proposed to improve quality of the molded articles and increase production efficiency. For example, Japanese Patent Kokai Publication No. 101322/1984 discloses supply of a resin melt through a resin conduit formed in a wall of a mold attached to a lower platen, namely a lower mold. Japanese Patent Kokai Publication No. 31929/1985 discloses supply of a resin melt through a resin conduit formed in a wall of a lower mold and closing the mold at a specific timing. However, both methods cannot completely prevent uneven gloss or small wrinkles which are so-called cold marks around the resin conduit having an opening on an inner wall of the mold. To suppress the formation of the cold marks, it may be contemplated to increase a resin temperature and/or a mold temperature. However, a time period from the finish of molding to the removal of the molded article from the mold becomes longer, so that a molding cycle is prolonged and in turn the productivity is worsened.
A multilayer molded article having a skin layer on the thermoplastic resin molded article to improve ornamental properties and functions of the article is widely used in various fields such as automobile interior panels or electric appliances. One of the methods for producing such multilayer molded article is disclosed in Japanese Patent Kokai Publication No. 235613/1989. In the conventional methods for producing the multilayer molded article including this method, since a high temperature resin melt is continuously supplied from a position close to the skin material, a part of the skin material is subjected to the high temperature for a longer time than other parts and then deteriorated and deformed so that various defects such as crush, unevenness or breakage of the skin material appear.